Spring中条件化的Bean

        @Conditional注解可以用到带有@Bean注解的方法上.如果给定的条件计算结果为true,才会创建这个Bean.

        例子如下:

package main.java.Demo1;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.type.AnnotatedTypeMetadata;

/**
 * @author [email protected]
 * @date 18-4-16 下午5:30
 */

public class CDPlayerExists implements Condition {
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        return false;
    }
}

package main.java.Demo1;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;

/**
 * @author [email protected]
 * @date 18-4-16 上午8:53
 */

@Configuration
public class CompactDiskConfig2 {
    @Bean
    public CompactDisc beatlesCD(){
        return new BeatlesCD();
    }

    @Bean
    @Conditional(CDPlayerExists.class)
    public CDPlayer cdPlayer(){
        return new CDPlayer(beatlesCD());
    }
}

        设置给@Conditional的类可以是任意实现了Condition接口的类型.要实现这个接口,只需实现matches()方法,若此方法返回true,则创建这个Bean.